Internet users would have to actively "opt-in" to view pornographic or harmful
content when they sign up for broadband or buy new mobile phones under plans
favoured by David Cameron.

Ministers are today launching a national consultation on a possible change in the law to give parents more control over the material their children view online.

The move follows concerns not only about sexually explicit material on the internet but also websites which promote suicide, self-harm, gambling or eating disorders.

A string of recent reports have also highlighted fears that the craze for “sexting” – sending explicit photographs by text message – or cyberbullying could be fuelling a hidden tide of sexual violence among children.

Parents and computer experts are being asked to choose between an automatic filter which would potentially harmful sites, but which could be switched off, or one in which people are forced to chose safety settings.

The so-called “active choice” system would give people the choice of blocking material such as 15 rated films or even social networking sites from a list when they sign up for a new broadband service, buy a new computer or set up a new smartphone.

A more robust form of the system, favoured by David Cameron, would “nudge” people to block some of the most harmful categories by having some items on the list ticked in advance.

It follows calls for better safeguards from the Government’s children’s tsar Reg Bailey, the chief executive of the Mothers’ Union, in a landmark report last year on the sexualisation and commercialisation of childhood.

Research by Ofcom, the media watchdog, found that a third of girls aged 14 to 16 have seen explicit photographs or videos, often filmed by their friends.

Despite rules preventing under-13s from using sites such as Facebook, children as young as eight are widely flouting the restrictions.

A quarter of children in their early teens regularly communicate with strangers through social networking sites.

But charities fear the true scale could be much higher.

A 10-week consultation on the plans is being launched by ministers today at a conference organised by the UK Council for Child Internet Safety (UKCCIS) attended by 150 organisations.

Tim Loughton, the children’s minister, said that forcing people to chose safety filters could prove more effective than automatically blocking material.

“There is no silver bullet to solve this, no filter can ever be 100 per cent foolproof,” he said.

“There is a cottage industry of people, mostly operating outside the UK, continually creating and proliferating ‘proxy’ websites that provide links to adult and harmful content.

“Automatic filtering on its own risks lulling parents into a false sense of security and there can never be any substitute for parents taking responsibility for how, when and where their children use the internet.”

He said that the internet industry needs to “raise its game” to ensure children are safe.

So far the four biggest internet service providers, BT, TalkTalk, Virgin Media and Sky, have already signed up to a new code of practice which would force all new customers to choose what filters they want when they first sign up.

But ministers have signalled that if the changes do not happen fast enough there will be legislation.

Mr Bailey, said last night that he was “delighted” that parents were being consulted.

“One of the things they told me during my research was that it was difficult to get their views heard," he said.

“I believe parents are best placed to manage what their children access online, what I’m looking for now is a model that is easier for them to manage.”

Andrew Flanagan, chief executive of the NSPCC, said: “Industry has done a huge amount in recent years and active choice is a step in the right direction.

“But long term we back the next step which is the introduction of an opt-in filtering system for all internet accounts in the UK, if necessary, supported by Government regulation.

“This will mean all new internet accounts will default automatically to a setting that blocks access to adult content.